High water temperature is a common problem in summer. There are many reasons for the high water temperature, and diagnosis is not simple. Usually, maintenance personnel will start the inspection from several easily faulty parts, such as the water temperature sensor, thermostat, radiator fan, etc. When these components are eliminated, maintenance personnel will suspect the radiator. 
The function of the radiator is to dissipate the heat from the coolant, ensuring that the engine operates within the normal working temperature range and preventing overheating. It is a very durable automotive component, so it will be inspected at the rear position. 

So, how do the maintenance personnel determine the quality of the radiator? 
1. Visual inspection 
The first thing to check is the appearance. Observe whether the radiator core is severely deformed or damaged, and whether the surface of the radiator core is severely dirty. You should know that if the radiator is too dirty, it will cause poor heat dissipation and also result in high water temperature. 
2. Leak Check 
Check if the radiator core and the upper and lower water pipe joints are leaking. After the coolant evaporates, obvious marks will be left. Also, inspect the clamps of the upper and lower water pipes of the radiator to ensure they are firmly fastened. Loose clamps are usually the main cause of leakage at this location. 
Additionally, if leakage cannot be detected through observation alone, a pressure test can be conducted to check for it, and a pressure tester is required. The pressure test can help us identify hard-to-detect leaks by applying pressure to the radiator to cause the coolant to leak from the leakage point, or by conducting a pressure retention test to check if the radiator can maintain pressure to confirm if there is any leakage. 
3. Check on the circulation status 
The blockage inside the radiator core will impede the flow of coolant and cause the engine to overheat. The blockage is usually caused by scale and rust on the radiator core. 
For vehicles with radiator caps, remove the radiator cap and start the engine to preheat it. When the engine reaches its operating temperature, that is, after the thermostat is turned on, you will see the coolant start to flow out from the opening. If you don't see the coolant flowing, it could be that the radiator is clogged, the thermostat is faulty, or the water pump is faulty. 
For vehicles without radiator caps, we can determine the cooling fluid circulation by checking the temperatures of the upper and lower radiator pipes. When the engine reaches its normal operating temperature, if there is a significant temperature difference between the upper and lower pipes, it indicates poor cooling fluid circulation. This could be due to a clogged radiator, a faulty thermostat, or a faulty water pump. 
Additionally, after the engine reaches its normal operating temperature, we can use an infrared thermometer to measure the temperature of the radiator core. If there is a significant temperature difference in certain areas, it indicates that the radiator may be clogged.